The present invention relates to truck brake mechanisms, and more particularly to a tool for adjusting backlash in such mechanisms.
A typical brake mechanism for large trucks comprises a pneumatic actuator coupled by a crank to a shaft, the shaft operating a brake shoe against a brake drum of a wheel of the truck. The brake shoe is biased away from contact with the drum. When the brakes are applied, the actuator is required to move a backlash distance corresponding to the clearance between the shoe and the drum before braking begins. Insufficient backlash causes dragging and overheating of the brakes. Excessive backlash introduces an undesirable delay in brake application and wastes precious high pressure air.
An adjustment screw is commonly provided on the crank for adjusting the backlash by changing the angular position, or phase, of the crank on the shaft. The adjustment is performed by turning the screw by means of a wrench. The adjustment is checked by comparing the distance moved by a connecting rod of the actuator between application and release of the brakes with a range of allowable backlash.
The importance of proper adjustment of truck brake mechanisms to trucking safety is recognized in that many states enforce a maximum limitation of the allowable brake mechanism backlash by in-route inspections, refusing further operation of offending rigs until they are properly adjusted.
A problem with the conventional adjustment provisions of the prior art is that two people are required to make the adjustment. A first person must observe the movement of the actuator and, if necessary, turn the adjustment screw, and a second person must apply and release the brakes of the truck. Several disadvantages are associated with this problem, for example:
1. The involvement of the second person is wasteful of manpower;
2. The first person risks injury in case the brakes are inadvertently operated while he is performing the adjustment, especially when the brake mechanism is in an awkward location and/or located far from the cab of the truck.
3. The inspection and/or adjustment is not possible when only one person is available, often the case when the truck is in route; and
4. The inspection and/or adjustment is not possible if the pneumatic power system is not operative, such as when a trailer having brakes to be serviced is not coupled to a tractor.
Another problem with the adjustment provisions of the prior art is that the adjustment screws are not standarized. As many as four different adjustment screw configurations are possible on a single rig comprising a tractor, two trailers, and a pair of bogie wheels, even when all the adjustment screws of a single unit are alike. The different screw configurations include variations in the location and orientation of the screw, as well as variations in both head size and type. Thus an assortment of wrenches must be carried by a person required to service the different truck brakes.
There is a need, therefore, for a tool for inspecting and adjusting truck brakes having any of several adjustment screw configurations and that can be safely used by an unassisted person without requiring pneumatic powered activation of the brakes.